In order to improve the wear resistance and elongate tool lifetimes, layers (or films) stacked of, for example, TiB2, B4C, SiC and the like are commonly formed on a surface of a substrate of a slide member or a metal cutting tool. Since a film made of a material such as TiB2, B4C and SiC has extremely high hardness (approximately 40 GPa), such a film formed on the surface of the slide member or of the metal cutting tool is called, for example, a hard film. Herein, a film formed by stacking a plurality of layers made of the above materials is particularly called a multilayer hard film. Here, various techniques of forming a hard film or a multilayer hard film using at least one layer made of TiB2, B4C, SiC, and the like are disclosed in Patent Literatures 1-5.
Patent Literature 1 discloses formation of a multilayer hard film made by stacking a TiB2 layer, a two-phase mixed layer of TiB2 and TiN phases, and a TiAlN layer in this order on a surface of a tool base formed of a cubic boron nitride-based material sintered under an ultrahigh pressure.
Patent Literature 2 discloses formation of a hard film on a surface of a base, where the hard film contains at least one TiB2 sublayer having a fibrous microstructure in which fibrous particles having a predetermined diameter and a predetermined length are oriented in the direction perpendicular to the surface of the base.
Patent Literature 3 discloses formation of a multilayer hard film made by stacking a BCN layer, a B4C layer, and a TiAlN layer in this order on a surface of a tool base formed of a cubic boron nitride-based material sintered under an ultrahigh pressure.
Patent Literature 4 discloses formation of a hard film made of SiC on a surface of a base.
Patent Literature 5 discloses a procedure for including at least one kind of ultramicroparticle made of a material selected from B4C, BN, TiB2, TiB, TiC, WC, SiC, SiNx (x=0.5 to 1.33), and Al2O3Al, into a hard film. The main component of the hard film is a nitride or a carbonitride of at least one kind of element selected from the Group 4A, Group 5A and Group 6A elements and Al.
The films disclosed in Patent Literatures 1-5 have high hardness and the wear resistance as well as other preferable properties via improvement of a stacked film. However, the difference in hardness between the substrate and the hard film leads to poor adhesion of the hard film to the substrate, which frequently terminates in the hard film peeling off the surface of the substrate. This results in a major drawback of a shortened lifetime of the cutting tool.
In order to overcome the above drawbacks, in Patent Literature 1, an attempt is made to improve the adhesion of hard films to substrates and to elongate the lifetime of the slide member by using the cubic boron nitride-based ultra high pressure-sintered material. Additionally, in Patent Literature 3, an additional attempt is made to further improve the adhesion of the film to the surface of the base which constitutes the tool and is formed of the cubic boron nitride-based ultra high pressure-sintered material, and elongate the lifetime of the base constituting the tool by forming the BCN layer between the B4C layer and the surface of the base (as a slide member) constituting the tool. Further, in Patent Literature 5, an attempt is made to improve the adhesion of the hard film and to elongate the lifetime of the slide member by including TiB2, B4C, SiC, and the like in the hard film.